Surprisingly I don't think there's been a scene from Citizen Kane nominated yet?
Nomination 7
Kane's Boyhood - Citizen Kane
Dir. Orson Welles 1941
I chose this scene for several reasons. It is arguably the most important scene of the film. It sets up Kane's entire future. The film comes full circle right back to this very important scene. The use of filming techniques is also top notch. Orson Welles was an amazing director, and brought so much to film. He definitely liked to play and experiment with different types of camera work, which can be seen here.
Spoiler: